Method of manufacturing a flexible film container

ABSTRACT

A method of manufacturing a flexible film container (10) from a flexible sheet of thermoplastic material. A gaseous mixture of fluoride gas and nitrogen gas is then introduced into the interior of the flexible film container, thereby expanding the flexible film container to an inflated configuration. The gaseous mixture is maintained within the flexible film container for approximately 15 seconds to 2 minutes so as to react to form a fluorinated barrier layer or surface. The fluoride gas is then removed from the flexible film container and the flexible film container is deflated to a collapsed configuration. The deflated flexible film container is then provided with a final seal and flattened for final shipment.

TECHNICAL FIELD

This invention relates to flexible film containers, and particularly to a method of manufacturing a flexible film container to prevent adverse reactions with material contents, the transmission of water vapor, or the passage of oxygen therethrough.

BACKGROUND OF THE INVENTION

Containers of all shapes and sizes are utilized to store and ship a large variety of items. Oftentimes, these items include liquids, grains, or powder which may react with the plastic material of the container. Accordingly, the container must be constructed to prevent the interaction between the reactive material contents and the container.

Rigid or semi-rigid containers have been constructed from a plastic which is treated with a fluoride gas to prevent the reaction of a liquid, grains, or powders with the plastic, transmission of water vapor, or the passage of oxygen through the container. The process of treating plastic with a fluoride gas may be referred to as fluorination. The fluorination occurs when the plastic container is initially blow molded from a hollow tube or parison to form the end product. The interior of a parison is injected with the fluoride gas which expands the parison within a mold wherein the expanded plastic parison takes on the shape of the mold. The interior surface of the rigid or semi-rigid plastic container reacts with the fluoride gas during the molding process to become fluorinated.

Flexible film containers made of a flexible film or sheet material have also been used to store materials. Flexible film containers are defined herein as a container which is readily flexible and is not considered to be of rigid or even semi-rigid construction. For example, a plastic bag used to contain liquid syrups in drink dispensers is considered to be a flexible film container, while a common plastic soda bottle is not considered to be a flexible film container but instead, is considered to be semi-rigid since it holds a definite shape even though it may be deformed, bent or made to flex only under pressure. The aforementioned plastic soda bottle is also not considered to be a flexible film container as it is not manufactured from a sheet of flexible film.

Flexible film containers have also been treated by fluorination to become non-reactive. In the past, the fluorination treatment of a flexible film container has commenced with the fluorination of the flexible sheet material prior to being formed into a container, as shown in U.S. Pat. No. 6,905,769. Alternatively, the flexible film material includes a fluorinated layer within a multi-layered or laminate sheet material is utilized to form the flexible film container, as shown in U.S. Patent Application Serial No. 2009/0301595.

A problem associated with the fluorination of flexible film is that the fluorinated treatment causes the film to become somewhat harder or stiffer, making it more difficult to weld. The fluorinated surface also must be the surface in contact with the liquid, therefor the fluorinated surface must be the interior surface of the flexible film container. However, in heat welding the flexible film to form the flexible film container it is the interior surfaces which are likely required to be melted to form the seal. With the fluorinated layer on the interior, it is proven to be more difficult to melt the hardened interior surface to form the seal without overheating the non-fluorinated outer surface of the plastic material.

Accordingly, it is seen that a need remains for a method of fluorinating a flexible film container formed from a flexible sheet or film material. It is to the provision of such therefore that the present invention is primarily directed.

SUMMARY OF THE INVENTION

A method of manufacturing a flexible film container comprises the steps of (A) providing a flexible thermoplastic sheet, (B) forming a flexible film container from the flexible thermoplastic sheet, (C) introducing a gaseous mixture of fluoride gas and at least one second gas into the interior of the flexible film container to expand the flexible film container to an inflated configuration, (D) maintaining the gaseous mixture within the flexible film container a sufficient time to cause the interior surface of the flexible film container to become fluorinated, and (E) removing the gaseous mixture from within the flexible film container to cause the flexible film container to deflate from the inflated configuration to a collapsed configuration.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a flexible film container made in a method embodying principles of the invention in a preferred form.

FIG. 2 is a schematic, top view of a flexible film container blank used in the manufacturing method of the flexible film container shown in FIG. 1.

FIGS. 3-5 are a series of perspective views showing the method of manufacturing or treating the flexible film container of FIG. 1.

DETAILED DESCRIPTION

With reference next to the drawings, there is shown a flexible film bag, liner, or container 10 embodying principles of the invention in a preferred form. The flexible film container 10 is shown in the configured of a rectangular prism, although it should be understood that the flexible film container can take on virtually any conventional shape of flexible film containers and is not limited by the preferred form shown in the drawings.

The flexible film container 10 has a bottom wall 12, four sidewalls 13, and a top wall 14. The flexible film container may also include any type of conventional fitment for the insertion or extraction of the contents within the flexible film container.

To form the flexible film container 10 a sheet of unfluorinated, flexible film, such as a single layer low density polyethylene (LDPE), linear low density polyethylene (LLDPE), or other plastics, is cut to form a blank 20, which is shown in schematic form and is not intended to represent any actual version of a blank used in the construction of a flexible film container. The blank is then manipulated or folded and sealed to form a complete or near complete flexible film container. The blank may be sealed by heat welding, radio frequency (RF) welding, or any other conventionally know method of sealing thermoplastic sheet material and the like. Alternatively, the flexible film container 10 may be formed from flexible lay flat tubing or any other conventionally know method of forming a flexible film container from a sheet of thermoplastic material.

Once the complete or near-complete flexible film container is formed, a gaseous mixture of fluoride gas and nitrogen gas is injected, forced, introduced or directed into the flexible film container, thereby expanding the flexible film container to an inflated condition or configuration as shown in FIG. 3. Preferably, the gaseous mixture is approximately 5% to 10% fluoride gas and approximately 90% to 95% of at least one second, preferably inert, gas such as nitrogen gas. However, it should be understood that the mixture and/or the use of additional secondary gases may vary depending upon the material used to form the blank and/or the specific material projected to be contained within the flexible film container. It is believed that the mixture should not have a fluoride gas percentage below approximately 3% and no more that approximately 20%.

It is believed that the gaseous mixture should be maintained within the flexible film container for approximately 15 seconds to 2 minutes, which is sufficient to allow the fluoride gas to react with the carbon molecules along the interior surface of the thermoplastic sheet material forming the flexible film container. The gaseous mixture may be flowed or deposited into the flexible film container with the use of a gas dispensing tube 25 positioned within the flexible film container or coupled to a fitment of the flexible film container.

The reaction between the fluoride gas and the carbon molecules forms a fluorinated barrier layer or surface which does not allow for the passage of liquids or gases, especially oxygen. The barrier layer or surface is substantially inert or non-reactive with chemicals which would otherwise react with the thermoplastic material forming the flexible film container. It should be understood that the introduction of fluoride gas into the flexible film container also kills germs contained within the flexible film container, making the flexible film container aseptic.

Once the gas mixture has been present within the flexible film container for the appropriate amount of time to fluorinate the interior surface, a quantity of fluorine free gas, such as nitrogen gas, is introduced into the interior of the flexible film container to flush or purge the fluorine gas from within the flexible film container. Once the purging is complete, the gas within the flexible film container is expelled or removed, as shown in FIG. 4, thereby deflating or evacuating the flexible film container to a fully or near-fully collapsed configuration, as shown in FIG. 5. The term near-fully collapsed configuration is used herein as it may be extremely difficult to remove all traces of gas from the interior of the flexible film container, as such, the term near-fully collapsed configuration is intended to mean a collapsed condition wherein substantially all, or at least a vast majority, of the gases are removed from within the flexible film container. The deflated flexible film container may then be collapsed, compressed or flattened by folding and compressing for final packaging and shipment.

Should the flexible film container include an inlet and/or outlet fitment, the fitment may be affixed either before or after the fluorination process. Also, in some instances the flexible film container may undergo a final sealing to completely seal the flexible film container.

As used herein, and in the claims, the term container may include both fully formed flexible film containers as well as near fully formed flexible film containers which lack the final sealing process after the flexible film container is filled with material.

It should be understood that other secondary gases may be used as an alternative to the nitrogen gas of the preferred embodiment. Preferably, the other secondary gas is an inert gas which will not react with the fluorine gas or the thermoplastic material of the flexible film container. While nitrogen gas is not a truly inert gas, as it reacts in only limited conditions, for purposes in most instances, as here, it is considered to be an inert gas. Lastly, the amount of fluorination depends on the exposure time to the fluoride gas, the temperature during exposure, and the concentration of the fluoride gas.

It thus is seen that a method of forming a fluorinated flexible film container is now provided which overcomes problems associated with flexible film containers of the prior art. While this invention has been described in detail with particular references to the preferred embodiments thereof, it should be understood that many modifications, additions and deletions, in addition to those expressly recited, may be made thereto without departure from the spirit and scope of the invention. 

1. A method of manufacturing a flexible film container comprising the steps of: (A) providing a flexible thermoplastic sheet; (B) forming a flexible film container from the flexible thermoplastic sheet; (C) introducing a gaseous mixture of fluoride gas and at least one second gas into the interior of the flexible film container to expand the flexible film container to an inflated configuration; (D) maintaining the gaseous mixture within the flexible film container a sufficient time to cause the interior surface of the flexible film container to become fluorinated, and (E) removing the gaseous mixture from within the flexible film container to cause the flexible film container to deflate from the inflated configuration to a collapsed configuration.
 2. The method of claim 1 wherein the second gas is an inert gas.
 3. The method of claim 2 wherein the inert gas is nitrogen gas.
 4. The method of claim 1 wherein the gaseous mixture is no more than 20% fluoride gas.
 5. The method of claim 1 wherein the gaseous mixture is no less than 3% fluoride gas.
 6. The method of claim 1 wherein the gaseous mixture is generally 5% to 10% fluoride gas.
 7. The method of claim 6 wherein the second gas is nitrogen gas.
 8. The method of claim 1 further comprising the step of (F) flattening the flexible film container for shipping purposes.
 9. The method of claim 1 wherein step (E) the removing of the gaseous mixture includes flushing the interior of the flexible film container with a fluorine fee gas, and subsequently removing substantially all of the remaining gas within the flexible film container.
 10. A method of manufacturing a flexible film container comprising the steps of: (A) providing an unfluorinated, flexible thermoplastic sheet; (B) forming the unfluorinated, flexible thermoplastic sheet into a flexible film container; (C) coupling a gas dispensing tube to the flexible film container; (D) flowing a gaseous mixture containing fluoride gas through the gas dispensing tube and into the flexible film container; (E) maintaining the gaseous mixture within the flexible film container to cause the interior surface of the flexible film container to become fluorinated; (F) removing the gaseous mixture from within the flexible film container; (G) collapsing the flexible film container, and (H) removing the gas dispensing tube from the flexible film container.
 11. The method of claim 10 wherein step (F) the removing of the gaseous mixture includes flushing the interior of the flexible film container with a fluorine free gas, and subsequently removing substantially all of the remaining gas within the flexible film container.
 12. The method of claim 10 wherein the gaseous mixture includes an inert gas.
 13. The method of claim 12 wherein the inert gas is nitrogen gas.
 14. The method of claim 10 wherein the gaseous mixture is no more than 20% fluoride gas.
 15. The method of claim 10 wherein the gaseous mixture is no less than 3% fluoride gas.
 16. The method of claim 10 wherein the gaseous mixture is generally 5% to 10% fluoride gas.
 17. The method of claim 16 wherein the second gas is nitrogen gas.
 18. The method of claim 1 further comprising the step of (I) compressing the flexible film container for shipping purposes.
 19. A method of manufacturing a flexible film container comprising the steps of: (A) providing a flexible polyethylene sheet; (B) forming a flexible polyethylene film container from the flexible polyethylene sheet; (C) inflating the flexible polyethylene film container by introducing a mixture of fluoride gas and at least one other gas into the interior of the flexible polyethylene film container; (D) maintaining the mixture within the flexible polyethylene film container to fluorinate the interior surface of the flexible polyethylene container, and (E) expelling the mixture from within the flexible polyethylene film container to cause the flexible polyethylene film container to fully or near-fully collapse.
 20. The method of claim 19 wherein step (E) the expelling of the mixture includes flushing the interior of the flexible polyethylene film container with a fluorine fee gas, and subsequently removing generally the remaining gas within the flexible polyethylene film container. 